I tend to lose a lot of melee units and sometimes too many mages. I can usually only battle 2 or 3 times before I have to wait for my whole front line to replenish. Currently my main Hero can grind until the refreshing units run out so I'm at 35 now and I'm actually a little uncomfortable going higher without a stronger portal. Any advice is greatly appreciated.

Leveling a Succubus is painful time-wise, there's no avoiding it. Especially if you opt to not waste mojo on lower level gear and spells (which is smart). It'll feel like you're not even fighting with a hero, just a big unit firing hero damage around.

As long as you keep your losses to footman and trolls and very rarely a mage (always keep a few mages in reserve), you're doing a good job, seriously.

This is from my experience leveling my Succubus to 30+:

Since upgrades increase both hp and damage, front-line troops benefit the most. I focused a majority upgrade gems on footman and trolls, then mages.

From level 12-21, trolls dominate the front as 98% of your battles will contain knights/mages/wolf riders, which trolls are way better than footman against. They're even decent ninja tanks. Footman are only useful vs archers. If the enemy has 2+ row of archers tanked by knights, I'd just pass on that fight.

At level 21, I bought Mystical Blast, which is an endgame spell. It helps, but your cooldown on it is still high so it's not game breaking.

Once you reach level 21, the Iron Wheel lets you use the build I nickname "The Cloth Grinder".

Shaman

Wheel

Wheel

Archer

Mage

Troll

Troll

Shaman

Wheel

Wheel

Archer

Mage

Troll

Troll

Shaman

Hero

Hero

Archer

Mage

Troll

Troll

Shaman

Hero

Hero

Archer

Mage

Troll

Troll

Shaman

Wheel

Wheel

Archer

Mage

Troll

Troll

Shaman

Wheel

Wheel

Archer

Mage

Troll

Troll

This build annihilates any comp level 20 or lower, and any higher level that don't use Iron Wheels yet. It's named so because enemies of that level consist of Knights and Mass cloth. With this build, mages take care of the knights, footman, and melee heroes, while mass piercing cuts through everything else. You only have to replace 12 trolls too.

You can still lose mages vs strong heroes and archers though, always make sure your mage count doesn't drop below 6, else waiting almost an hour for mages is a big slowdown.

The problem is if you're facing Iron Wheels, but that's when footman make their return to your forces of course! Mix them in as necessary. If I face a mixed Iron Wheel/Wolf Rider back line, I just skip the battle.

As you advance higher and higher, this build becomes obsolete as Archangels, Iron Wheels, and Archangels are all extremely resistant to piercing damage. By then you will want to convert your frontline to footman and cyborg+priest to combat them. Also, hopefully you have a strong succubus to take off the pressure too. You can even have her tank some lanes in front of you're geared enough.

It's a tough, long grind, but if you stick to it, you'll have arguably the best end-game hero on your side.

@Threshen: at beginning level, you can put her on front line to be tanker, with 2 Priest back her up. You can put 2 footman infront of her to avoid the enemy's firepower focus on her at first time. I did it with my Succ and it works well, just use the Ivy set, and add just 1 point to Def, and ~10 points to HP.When you have the aid of high-level Mage + Shaman and some awesome dps such as Iron Wheel (lv 21), you can put her back with shammy behind her.